Severe acute and chronic pains refer to the nociception and painful sensation resulted from stimulation of nociceptors by a variety of injury stimuli passed to the central nervous system by the impulse of messenger of nociceptive transmission. Severe acute and chronic pains, including cancer pains, postoperative pains, a variety of repeated episodes of acute and chronic pains, trouble tens of millions of patients, and constitute a major clinical problem.
Clinical analgesics can be divided into three categories: 1) non-steroidal anti-inflammatory analgesic, 2) opioid analgesics, and 3) other non-opioid analgesics, including local anesthetics, anti-depressants, antiepileptic drugs, etc.
Currently, acute pains and cancer pains are mainly treated with opioid analgesics clinically. Broad application of opioid analgesic drug is limited due to its side effects such as addiction, respiratory depression and reduced gastric movement. Treatment of a variety of chronic non-cancer pains and neuropathic pains with opioid analgesics or non-steroidal anti-inflammatory drugs is hardly satisfying. Therefore, the search of broad-spectrum analgesic drugs having a strong analgesic effect while overcoming many side effects of opioid and non-steroidal anti-inflammatory analgesic drugs has become the primary goal of the field and the focus of innovative pharmaceutical research.
In recent years, some large pharmaceutical companies abroad, such as Merck and Pfizer, etc., have invested heavily in the development of new non-narcotic central analgesics, and have made some progress. For example, in 2005 the U.S. FDA approved the listing of calcium channel blocker Ziconotide for the treatment of severe chronic pains that cannot be treated with or is tolerated by other drugs. This drug can lead to side effects such as orthostatic hypotension.
Existing drugs are far from meeting the clinical needs of pain control for different patients. Especially for certain types of cancer pains, severe chronic pains, and some neuropathic pains, there exists no suitable, safe and effective analgesic drug. Thus, development of non-narcotic analgesics with novel chemical structure having mild or no side effects, broad application, and clinical safety, continues, in order to meet the needs of different patients with pain. Meanwhile, non-opioid analgesics have a huge growing market and, if novel analgesics come out, they will have large social and economic benefits.